Synaptogenesis in fetal human retinas is being studied by electron microscopy with the emphasis on the earliest detectable changes in photoreceptor synapses and formation of synaptic ribbons. The retinas of several species of squirrels are being studied by light and electron microscopy. The emphasis is on photoreceptor structure, outer segment renewal, and outer plexiform layer structure. Protein renewal in these photo-receptors will be studied by autoradiography. The developing and adult Xenopus retina will be examined by electron microscopy and synaptic density in the inner plexiform layer determined from montages. The effect of various metabolic inhibitors on development of the Xenopus visual system will also be studied. Pigmented cells in Bulla Gouldiana are being studied with reference to the pigment a granule-lysosome system. The response of these cells to light will be examined by intracellular recording and the pigment will be isolated and characterized.